In a metal enclosed switchgear having a large current capacity rating, conductor temperature and ambient air temperature increase by Joule heat generation due to energization to main circuit conductors and induction heat generation of a structural object around the conductors. In order to suppress this temperature rise to a certain level, the air around the switchgear is taken in to lower internal air temperature by convection in the inside of the switchgear. In order to maintain a conductor portion or the like to be equal to or lower than a certain temperature, a structure is generally devised such that an air intake opening is provided at a relatively low position of the back surface and/or the front surface of the switchgear and an air discharge opening is provided in a ceiling portion to increase ventilation efficiency by use of a head difference between the air intake and the air discharge openings in addition to the convection in the switchgear.
Although extremely rare, during operation of the switchgear, an electrical fault may occur in the main circuit in the inside of the switchgear due to various causes. When the electrical fault occurs, an arc is generated at that portion; and by arc energy thereof, a rapid internal pressure rise and high temperature and high pressure gas are generated.
In a conventional metal enclosed switchgear having a relatively small current rating, air intake and discharge openings for ventilation are not generally provided; and accordingly, when high temperature and high pressure gas is generated in the inside, the high temperature and high pressure gas is discharged outside the switchgear from a pressure relief opening provided in a ceiling of the switchgear by only opening a pressure relief plate. In this regard, however, in a switchgear having a large current rating, high temperature gas is blown out from not only a pressure relief opening and an air discharge opening portion for ventilation in a ceiling portion, but also an air intake opening provided in the rear surface or the front surface of the switchgear.
Basically, the pressure relief opening during a fault is provided; and therefore, the blowout of the high temperature gas during the fault from the air discharge opening for ventilation in the ceiling portion of the switchgear is not a problem even when the high temperature gas is blown out therefrom. However, the blowout of the high temperature gas from the air intake opening for ventilation provided in the back surface or the front surface of the switchgear needs to be suppressed.
Thus, for example, a switchgear shown in Patent Document 1 and Patent Document 2 is made such that a check valve type shutter provided on an air intake opening portion operates in response to an internal pressure rise due to an abnormal internal pressure rise during a fault of the switchgear and blocks the air intake opening from the inside. This prevents the high temperature and high pressure gas from flowing back in a ventilation path and releasing to the periphery of the switchgear.